Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats


Appendix I.

771

of expansion and compression between these temperatures are
•strict adiabatics.

The second and only* other method of obtaining reversibility
is to use a regenerator, as first practically attempted by Stirling, and
•afterwards by Ericsson in their respective air engines. Diagram
-A, Fig. 757, shews Stirling's cycle. The gas having a pressure

STIRLING S
fUR ENGINE

(A)

and volume corresponding to #, took in heat along the isothermal
-a b; rejected a portion during b c to the regenerator, at constant
volume; was compressed isothermally from c to d, during which
time heat was rejected to a refrigerator; and between d and a
again received the heat which was rejected from b to c. Although
«J> c and d a are substituted for adiabatics, the giving and receiving
of heat is strictly within the engine itself, the heat rejected, at b c
-being fully returned at d a, so the reversibility is unimpaired.
Diagram B illustrates the cycle of Ericsson, which is only
-different from that of Stirling in that the regenerator gives or
abstracts heat at constant pressure. As before, a may be con-
sidered the starting-point. * (Excepting as in Apfendix If.,
A 883.)

P. 613. Reversibility in the Steam Engine. — It
appears, therefore, that supply and rejection must be along
isothermals, and expansion and compression along adiabatics
(unless a regenerator be used). Remembering that isothermals
fbr saturated steam are horizontal straight lines, the reversible
cycle in Fig. 758 for the steam engine is easily understood.
Thus a b is the isothermal of reception, b c the adiabatic of
expansion, cdiht isothermal of rejection, and da the adiabatic